Upon an inquiry into the validity of a verdict or indictment, a juror may not testify as to any matter or statement occurring during the course of the jury's deliberations or to the effect of anything upon his or any other juror's mind or emotions as influencing him to assent to or dissent from the verdict or indictment or concerning his mental processes in connection therewith, except that a juror may testify on the question whether extraneous prejudicial information was improperly brought to the jury's attention or whether any outside influence was improperly brought to bear upon any juror. Nor may his affidavit or evidence of any statement by him concerning a matter about which he would be precluded from testifying be received for these purposes.

Some courts have held that jurors' use of a dictionary to define the elements of a crime or words in jury instruction does not constitute the use of extraneous prejudicial information because their use of the dictionary is for the purpose of defining a legal term rather and does not relate to "facts under deliberation." See, e.g., United States v. Cheyenne, 855 F.2d 566, 568 (8th Cir. 1988). Other courts have held that jurors' use of a dictionary is not inherently prejudicial but have noted that in rare cases such use can require a new trial. See, e.g., United States v. Henley, 28 F.3d 1111, 1115-16 (9th Cir. 2001). Finally, some courts have found that it's quite possible that jurors' use of a dictionary can require a new trial, especially when jurors use the dictionary to define legal terms. See, e.g., Sharrief v. Gerlach, 798 So.2d 646, 652 (Ala. 2001).

As the recent opinion of the Court of Appeals of North Carolina in State v. Patino, 2010 WL 3860847 (N.C.App. 2010), makes clear, North Carolina courts (kind of) fall under the first category of courts.

In Patino, Jonathan Patino was convicted of sexual battery. Thereafter,

the day after the verdict was delivered, at the start of the sentencing hearing, defendant's trial counsel moved for a new trial and told the trial court that several jurors had spoken with defense counsel and admitted looking up various legal terms (sexual gratification, reasonable doubt, intent, etc.), as well as the sexual battery statute, on the Internet during the trial. Defense counsel contended that the jury committed misconduct by consulting outside sources of information and disobeying the trial court's instruction not to do so. The trial court did not conduct any further inquiry and denied defendant's motion.

After he was sentenced, Patino appealed this and other rulings, and the Court of Appeals of North Carolina affirmed, finding that

Because definitions of legal terms are not extraneous information under Rule 606 and did not implicate defendant's constitutional right to confront witnesses against him, the allegations raised by defendant's trial counsel were not proper matters for an inquiry by the trial court. Thus, the trial court did not abuse its discretion in failing to conduct further inquiry into the allegations or in denying defendant's motion for a new trial.

I don't see the logic of the Court of Appeals of North Carolina. Extraneous prejudicial information is generally thought to be "information that was not admitted into evidence but nevertheless bears on a fact at issue in the case." Robinson v. Polk, 438 F.3d 350, 363 (4th Cir. 2006). Now, dictionary definitions might not be prejudicial because they might not bear upon facts at issue in cases. But I don't see how they could be defined as anything but external in that they are information not presented at trial. I also think that they are prejudicial because they can compete with the legal definitions involved in a trial (e.g., the legal definition of "sexual gratification" could be quite different from the dictionary definition of "sexual gratification"). But I can at least see the logic of courts reaching the opposite conclusion. BuI don't see the logic of defining dictionary definitions as anything but external information.